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Autosomal Inheritance

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Topics

  • Autosomal Inheritance
  1. Widow’s peak
  2. Phenylketonuria (PKU)

Notes

Introduction of Autosomal Inheritance:  

  • Human somatic (2n) cell contains 23 pairs of chromosomes. They can be divided functionally as autosomes and sex chromosomes.  
  • Autosomes control a variety of traits other than sex. These traits are called autosome linked traits 
  • Transmission of body characters other than the sex-linked traits from parents to their offsprings through autosomes, is called autosomal inheritance. 
  1. Widow’s peak:
  • A prominent “V” shaped hairline on forehead is described as widow’s peak. It is determined by autosomal dominant gene.  
  • Widow’s peak occurs in homozygous dominant (WW) and also heterozygous (Ww) individuals. Individuals with homozygous recessive (ww) genotype have a straight hair line (no widows peak). Both males and females have equal chance of inheritance 
  1. Phenylketonuria (PKU): 
  • It is an inborn metabolic disorder caused due to recessive autosomal genes. When recessive genes are present in homozygous condition, phenylalanine hydroxylase enzyme is not produced.  
  • This enzyme is essential for conversion of amino acid phenylalanine into tyrosine. Due to absence of this enzyme, phenylalanine is not converted into tyrosine.  
  • Hence, phenylalanine and its derivatives are accumulated in blood and cerebrospinal fluid (CSF). It affects development of brain and causes mental retardation.  
  • Excess phenylalanine is excreted in urine, hence this disease is called phenylketonuria. 
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